[91 中山光电] 题目 : Find the function f(x,y) satisfying the Laplace equation d^2 f d^2 f ------- + ------- = 0 , for x^2 + y^2 = a , a > 0 d^2 x d^2 y and the boundary condition f(x,y) = x^3 for x^2 + y^2 = a 3 1 答案 : f = --- a r cosθ + --- r^3 cosθ 4 4 不知道该如何把边界条件换成柱座标，麻烦板上高手帮忙指导一下，谢谢 --

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